The objectives of the proposed study are: (1) to establish the relative importance of vasomotion upon the energy balance of chickens and (2) to investigate the role of the central nervous system upon the partitioning of blood through the capillaries or the arteriovenous anastomoses (AVA's). The importance of vasomotion will be determined by direct measurements of convective and radiant heat loss using partitional gradient layer calorimetry. Two "organ" calorimeters will be constructed to measure heat loss from the two major sites of known vasomotor control--feet and head. Heat loss from the feathered surfaces will be measured by the existing calorimeter. Attention will focus on the foot because it is ideally suited for vasomotion studies, having a large surface to volume ratio, is uninsulated, has a simple system of nerves and blood vessels, has few muscles, and no sweat glands. The heat given up by the blood as it passes through the foot will be measured by monitoring temperature and blood flow of the blood entering the foot, the temperatures of the blood leaving the foot via the two major venous routes, and the blood flow of one of these two routes. These data will be used to formulate a model, which can be used to assess the effect of air movement over the feet and the effect of covering the feet as when the hen sits down. Spontaneous vasomotor control and induced vasomotor control will be monitored below, at and above thermoneutrality of unanesthetized chickens. To induce both vasoconstriction and vasodilation we will heat and cool the spinal cord or the hypothalamus or both. Vasomotion due to the altered vascular resistance of the capillaries or the AVA's will be monitored via two ultrasonic doppler flow probes, chronically implanted at the major incoming artery to the foot and the veins which drain the AVA's. Vasomotor control by higher centers will be ascertained by injecting alpha-and beta-adrenergic vasoactive chemicals, which are believed to differentially select between the capillaries and the AVA's.